Chpwn has uncovered references in iOS 3.x to the vile Carrier IQ rootkit that has recently been discovered in Android devices. He notes that that it is possible that the service is not enabled by default, and that the iOS variant seems to be less nosey than its Android counterpart. Chpwn will be doing a detailed report on his findings, including what data is actually being transmitted and what iOS versions are affected. Carrier IQ is suspected of phoning home private information such as call log, location, and app data to carriers—but iOS users may not need to worry just yet.
However, from what I can tell /so far/, Carrier IQ /may/ only enabled on the iPhone when diagnostic logging is enabled.